docs: def get_facet_serializer_class(self):
          """
          Return the class to use for serializing facets.
          Defaults to using ``self.facet_serializer_class``.
          """
          if self.facet_serializer_class is None:
              raise AttributeError(
                  "%(cls)s should either include a `facet_serializer_class` attribute, "
                  "or override %(cls)s.get_facet_serializer_class() method." %
                  {"cls": self.__class__.__name__}
              )
          return self.facet_serializer_class